The nature of the vascular response to acetylcholine is tissue and species specific. Acetylcholine produces vasoconstriction in the pulmonary vasculature of rabbits and dogs and cycloxygenase inhibitors totally prevent or potentiate the response, respectively. The feline and bovine pulmonary vasculatures relax in response to actylcholine as do systemic vasculatures in all species tested. Acetylcholineinduced relaxation of many, but not all, vessels is mediated through the release of endothelium derived relaxing factor(s). Preliminary studies in our laboratory have uncovered differences in inhibition by muscarinic receptor subtype selective antagonists of the response to acetylcholine among vessels of different size and origin. Furthermore, we have demonstrated the existence and began characterizing muscarinic binding sites on bovine pulmonary arterial endothelial in culture. The proposed investigation will test the hypothesis that the localization, density, subtype or transduction mechanisms of endothelial or smooth muscle muscarinic receptors is different in vessels of different size and origin (bed or species). We propose to employ muscarinic receptor subtypeselective antogonists (pirenzepine, gallamine, secoverine, trihexiphenidyl, 4DAMP) to systematically characterize pulmonary and systemic endothelial and smooth muscle cell muscarinic receptors and their association with the activation of possible messengers (arachidonate metabolites, cyclic nucleotides, endothelium derived relaxing factor, inositol phosphate turnover, calcium influx). We will correlate receptor properties to type and amounts of messengers activated, in fresh isolates and cultures of endothelial and smooth muscle cells from large and small pulmonary artery, large and small pulmonary vein, aorta and mesenteric artery of rabbit, small pulmonary artery of cat and dog, vessels chosen for their diverse response to muscarinic stimulation. We will also correlate second messenger production in the different cell lines to the physiological response of the vessel in order to reveal possible selectivity of the biochemical pathways for each response.